Subtypes of dementia of the Alzheimer type (DAT) - DAT with motor abnormalities, such as extrapyramidal signs (EDAT) and myoclonus (MDAT), were studied using neurochemical measurements in the cerebrospinal fluid (CSF). Reductions in somatostatin-like immunoreactivity (SLI) and acetylcholinesterase (AChE) activity were found in DAT, EDAT and MDAT. The latter two groups had deficits in the monoaminergic neurotransmitter systems, seen as reduced CSF homovanillic acid (HVA) and the hydroxylation cofactor, biopterin. MDAT patients also had reduced CSF 5-hydroxyindoleacetic acid (5-HIAA). Compared to age-matched control subjects, early-onset DAT patients have reductions in CSF AChE activity, and late-onset DAT patients have reductions in CSF alpha-melanocyte stimulating hormone-like immunoreactivity (alpha-MSH-LI). An inverse relation between CSF HVA and alpha-MSH-LI was found in DAT patients. Furthermore, in patients with Parkinson's disease, CSF alpha-MSH-LI was elevated. Young adult Down syndrome subjects had elevated levels of CSF choline, but AChE activity and somatostatin and neuropeptide Y concentrations did not differ from control values in either young or old Down patients. In healthy control subjects, age-related increases were found in CSF total protein, choline, the polyols erythritol and myoinositol, and AChE activity.